1. Field of Invention
This invention relates generally to novel adjuvant formulations for enhancing the immune response to antigens for use in immunogenic and vaccine compositions, without producing toxic or undesirable side effects in the subject. This invention also relates to methods of preparation and use of the adjuvant, immunogenic, and vaccine compositions.
2. History and Description of Related Art
Bacterial, viral, and parasitic infections are wide spread in humans and animals. Diseases caused by these infectious agents are often resistant to antimicrobial pharmaceutical therapy, leaving no effective means of treatment. Consequently, a vaccinology approach is increasingly used to control infectious disease. A whole infectious pathogen can be made suitable for use in a vaccine formulation after chemical inactivation or appropriate genetic manipulation. Alternatively, a protein subunit of the pathogen can be expressed in a recombinant expression system and purified for use in a vaccine formulation. Vaccines can be made more efficacious by including an appropriate adjuvant in the composition.
There is also an increased interest in using a vaccinology approach for treating cancer in animals and humans. This therapeutic approach to the treatment of cancer involves vaccinating cancer patients with a vaccine comprising a tumor-specific antigen and an adjuvant. However, none of the many cancer vaccines of this nature in development has been approved by regulatory authorities. Vaccines have not been shown to shrink tumors, a standard measure of a cancer drug's effectiveness.
The term ‘adjuvant’ generally refers to any material that increases the humoral or cellular immune response to an antigen. Adjuvants are used to accomplish two objectives: They slow the release of antigens from the injection site, and they stimulate the immune system. Traditional vaccines are generally composed of a crude preparation of inactivated or killed or modified live pathogenic microorganisms. The impurities associated with these cultures of pathological microorganisms may act as an adjuvant to enhance the immune response. However, the immunity invoked by vaccines that use homogeneous preparations of pathological microorganisms or purified protein subunits as antigens is often poor. The addition of certain exogenous materials such as an adjuvant therefore becomes necessary. Further, synthetic and subunit vaccines are expensive to produce. The addition of an adjuvant may permit the use of a smaller dose of antigen to stimulate a similar immune response, thereby reducing the production cost of the vaccine. Thus, the effectiveness of some injectable medicinal agents may be significantly increased when the agent is combined with an adjuvant.
Many factors must be taken into consideration in the selection of an adjuvant. An adjuvant should cause a relatively slow rate of release and absorption of the antigen in an efficient manner with minimum toxic, allergenic, irritating, and other undesirable effects to the host. To be desirable, an adjuvant should be non-viricidal, biodegradable, capable of consistently creating a high level of immunity, capable of stimulating cross protection, compatible with multiple antigens, efficacious in multiple species, non-toxic, and safe for the host (eg, no injection site reactions). Other desirable characteristics of an adjuvant are that it is capable of micro-dosing, is dose sparing, has excellent shelf stability, is amenable to drying, can be made oil-free, can exist as either a solid or a liquid, is isotonic, is easily manufactured, and is inexpensive to produce. Finally, it is highly desirable for an adjuvant to be configurable so as to induce either a humoral or cellular immune response or both, depending on the requirements of the vaccination scenario. However, the number of adjuvants that can meet the above requirements is limited.
The choice of an adjuvant depends upon the needs for the vaccine, whether it be an increase in the magnitude or function of the antibody response, an increase in cell mediated immune response, an induction of mucosal immunity, or a reduction in antigen dose. A number of adjuvants have been proposed, however, none has been shown to be ideally suited for all vaccines. The first adjuvant reported in the literature was Freund's Complete Adjuvant (FCA) which contains a water-in-oil emulsion and extracts of mycobacterium. Unfortunately, FCA is poorly tolerated and it can cause uncontrolled inflammation. Since the discovery of FCA over 80 years ago efforts have been made to reduce the unwanted side effects of adjuvants.
Some other materials that have been used as adjuvants include metallic oxides (e.g., aluminum hydroxide), alum, inorganic chelates of salts, gelatins, various paraffin-type oils, synthesized resins, alginates, mucoid and polysaccharide compounds, caseinates, and blood-derived substances such as fibrin clots. While these materials are generally efficacious at stimulating the immune system, none has been found to be entirely satisfactory due to adverse effects in the host (e.g., production of sterile abcesses, organ damage, carcinogenicity, or allergenic responses) or undesirable pharmaceutical properties (e.g., rapid dispersion or poor control of dispersion from the injection site, or swelling of the material).
Synthesized oils and petroleum derivatives have been used as adjuvants because they exhibit relatively slow dispersion in the body, but they may be undesirable as they frequently are broken down into aromatic hydrocarbons, which may be carcinogenic. Furthermore, some of these substances have been found to be capable of producing sterile abcesses and may never be completely eliminated by the body. Oils when appropriately selected and formulated at proper concentrations can be relatively safe and nontoxic.
Saponins obtained from bark of the South American tree Quillaja saponaria have been used as adjuvants for some time. See Lacaille-Dubois, M and Wagner H. (A review of the biological and pharmacological activities of saponins. Phytomedicine vol 2 pp 363-386. 1996). Many of the veterinary vaccines in use today contain Quil A, which is the saponin fraction from the bark of the South American tree Quillaja saponaria molina. Further fractionation of Quil A has yielded sub-fractions, including QS-7, QS-17, QS-18, and QS-21. (See U.S. Pat. No. 5,057,540)
The use of saponins as adjuvants is associated with a number of disadvantages. Saponins are soluble and thus stimulate a non-specific immune response. The goal of vaccinology, however, is to stimulate a targeted response to a specific antigen or antigens. Saponins have a strong affinity for cholesterol. They form a complex with the cholesterol found in cell membranes causing hemolysis of the cell. They have also been shown to cause necrosis at the injection site and to be difficult to formulate into particulate structures. When used in vaccines containing modified live enveloped viruses, saponins disrupt the viral envelope and thereby inactivate the viral antigens.
To overcome the hemolytic and viricidal properties of Quil A, it has been combined with cholesterol and phospholipids, which form a specific structure known as an immunostimulatory complex (ISCOM) or ISCOM matrix (ISCOMATRIX). See Ozel M., et. al.; J. Ultrastruc. and Molec. Struc. Re 102, 240-248 (1989). ISCOMs, when combined with an antigen, generally induce a Th1 cytotoxic T-cell response. However, while greatly reducing the hemolytic properties of Quil A, combining Quil A with cholesterol does not completely eliminate them. Another limitation of ISCOMs is that a protein antigen must have hydrophobic domains large enough to interact with the ISCOM in order to be incorporated into an ISCOM. A protein which is highly hydrophilic cannot be incorporated into an ISCOM. Finally, ISCOMs can stimulate an undesirable autoimmune reaction in the subject.
Immunomodulators have been used as adjuvants, with examples including dimethyl dioctadecyl ammonium bromide (hereinafter, “DDA”), and avirdine. DDA is a lipophilic quaternary ammonium compound (amine) with two 18 carbon alkyl chains and two methyl groups bound to a positively charged quaternary ammonium molecule with a molecular weight of 631. Its use as an adjuvant was discovered by Gall, (Immunol. V. 11, p. 369,1966). DDA is reported to stimulate strong cell mediated immune responses, and has also been shown to induce humoral immune responses. Many papers have been published showing efficacy of DDA as an adjuvant for protein antigens, haptens, tumors, viruses, protozoa and bacteria. (See Korsholm, K S., et al., Immunology, vol. 121, pp. 216-226, 2007.) Most studies have been performed in laboratory animals, while only a few have been carried out in larger animals such as chickens (See Katz, D., et al. FEMS Immunol Med Microbiol. Vol 7(4):303-313, 1993.), pigs, and cattle. DDA is effective in inducing a delayed-type hypersensitivity (DTH) reaction in both laboratory animals and large animals. However, it is poorly soluble in water.
Polymers have also been used as adjuvants, with examples including diethyl-aminoethyl (DEAE)-dextran, polyethelyne glycol, and polyacrylic acid (e.g., CARBOPOL®). The polysaccharide DEAE-dextran is known in the art as a very strong adjuvant. However, it has been associated with unacceptable reactogenicity. CARBOPOL® polymers are polymers of acrylic acid cross-linked with polyalkenyl ethers or divinyl glycol. CARBOPOL® has been used in a number of vaccines, but its use as an adjuvant has not been proven.
Some adjuvants have been shown to stimulate a Th2 response, with examples including N-(2-Deoxy-2-L-leucylamino-b-D-glucopyranosyl)-N-octadecyldodecanoylamide hydroacetate, also known by the trade name Bay R1005® when in its acetate form, and aluminum. Bay R1005® in combination with purified virus vaccines or subunit vaccines led to increased production of antibody in virus-challenged mice. Preclinical trials in other animal species (pig, sheep, horse) gave comparable results with respect to antibody production. The increase in antibody synthesis induced by Bay R1005® is specifically dependent on the antigen and is not the result of polyclonal stimulation.
Prior to this invention, no adjuvant formulation possessed the broad range of desirable characteristics an ideal adjuvant should have. There has been an effort to find new adjuvants for vaccines that would overcome the deficiencies of conventional ones. In particular, an adjuvant formulation which elicits potent cell-mediated and humoral immune responses to a wide range of antigens in humans and animals, yet lacks the side effects and formulation difficulties of conventional adjuvants, is highly desirable.